RAM snapshots feature

This patch adds the ability to take live snapshot of a VM that includes
its memory state, and to restore memory state that is saved as part of a
snapshot when reverting back to it.

There is a detailed description of the design at the feature page:
http://wiki.ovirt.org/Features/RAM_Snapshots

Change-Id: I62401940afb0228cbd9dd3611b6ed8e0ff67c82c
Signed-off-by: Arik Hadas <ahadas@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/15072
Reviewed-by: Yeela Kaplan <ykaplan@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>